The present invention is directed to ink compositions, and more specifically, the present invention relates to hot melt inks especially useful for ink printing, processes and apparatuses, reference for example U.S. Pat. No. 5,121,141, U.S. Pat. No. 5,111,220, U.S. Pat. No. 5,128,726, U.S. Pat. No. 5,371,531, U.S. Ser. No. 176,381 now abandoned, and U.S. Pat. No. 5,528,384, the disclosures of which are totally incorporated herein by reference, including especially acoustic ink processes as illustrated in some of the aforementioned copending applications and patents, such as an acoustic ink printer for printing images on a recording medium, comprising a source of several different-colored liquid inks cyan, magenta, yellow, and black (C, M, Y, K), which source possesses a free surface proximate to the recording medium with each of the different-colored inks appearing on the free surface in a predetermined order; an acoustic printhead adapted to be acoustically coupled to the source for radiating the ink appearing on its free surface with focussed acoustic energy, whereby radiation pressure is exerted against the different colored inks on the free surface, and a controller coupled to the printhead for modulating the radiation pressure exerted against the free surface of said source in accordance with data representing an image, whereby droplets of the different-colored ink are able to be ejected on command from the different bodies to fall on the recording medium.
More specifically, the present invention is directed to hot melt acoustic ink compositions wherein there can be generated with such inks excellent images with acceptable image permanence, excellent projection efficiency on transparencies with, for example, raised wax bump matte type images without a post fusing step, or without a post pressure treatment to flatten the bumps, and excellent crease resistance, and wherein the inks possess acceptable, and in certain embodiments superior lightfastness, and superior waterfastness. Moreover, in embodiments of the present invention there is enabled low MFLEN (mean frequency line edge noise), or edge acuity, for example a MFLEN of less than about 3, and more specifically, from about 0.5 to about 2.8, low intercolor bleed (ICB) of less than about 10, and more specifically, from 1 to about 5, and the elimination, or minimization of undesirable paper curl since water is not present, or very small amounts thereof are selected, in the invention inks, and in this regard it is preferred that there be an absence of water, and since water is not present in the inks a dryer can be avoided thereby minimizing the cost of the acoustic ink jet apparatus and process. The inks of the present invention in embodiments thereof are comprised of a copolymer vehicle, and more specifically, a triblock copolymer including, for example, certain physically crosslinked and physically branched networks, and wherein the networks can form a tough extended structure at room temperature, for example from about 20.degree. C. to about 30.degree. C. and preferably about 25.degree. C., and wherein on heating the extended structure to the jetting temperature the physical crosslinks, or the physical branch points break to provide dissociated low molecular weight chains with low viscosity suitable for jetting. The aforementioned physical crosslinks, or physical branch points can be formed by association of endgroups of diblock and triblock copolymers wherein association is by hydrophobic bonds, hydrogen bonds, other known physical association mechanisms, and the like. With acoustic ink printing, it is desirable that the printheads be operable, for example, at a maximum temperature of about 160.degree. C., and the jettability/throughput requirements may limit the viscosity of the ink to for example about 10 centipoise (centipoise) at the about 160.degree. C. jetting temperature and these and other needs are achievable with the inks, and processes of the present invention in embodiments thereof.
Ink jet printing systems generally are of two major types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or to a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems, which use piezoelectric devices to expel the droplets, also suffer the disadvantage of a slow printing speed.
The other type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system is initiated with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink, in excess of the normal boiling point, diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction toward a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
Ink jet printing processes may also employ inks that are solid at room temperature and liquid at elevated temperatures. For example, U.S. Pat. No. 4,490,731, the disclosure of which is totally incorporated herein by reference, discloses an apparatus for dispensing certain solid inks for printing on a substrate such as paper. The ink dye vehicle is selected to have a melting point above room temperature so that the ink, which is melted in the apparatus, will not be subject to evaporation or spillage during periods of nonprinting. The vehicle is also chosen to have a low critical temperature to permit the use of the solid ink in a thermal ink jet printer. In thermal ink jet printing processes employing hot melt inks, the solid ink is melted by a heater in the printing apparatus and utilized as a liquid in a manner similar to that of conventional thermal ink jet printing. Upon contact with the printing substrate, the molten ink solidifies rapidly, enabling the dye to remain on the surface instead of being carried into the paper by capillary action, thereby attempting to enable higher print density than is generally obtained with liquid inks. Advantages of a hot melt ink in ink jet printing are the substantial elimination of potential spillage of the ink during handling, a wide range of print density and quality, minimal paper cockle or distortion, and enablement of indefinite periods of nonprinting without the danger of nozzle clogging, even without capping the nozzles. Hot melt ink jets are dissimilar than thermal ink jets described, however, a hot melt ink contains no solvent or water. Thus, rather than being liquid at room temperature, a hot melt ink is typically a solid or semi-solid having a wax-like consistency. These inks usually, thus as indicated herein, may need to be heated to approximately 100.degree. C. before the ink melts and turns into a liquid. As with the thermal ink jet, a plurality of ink jet nozzles are provided in a printhead. A piezoelectric vibrating element is located in each ink channel upstream from a nozzle so that the piezoelectric oscillations propel ink through the nozzle. After the hot melt ink is applied to the substrate, the ink is resolidified by freezing on the substrate.
Each of these types of known ink jets, however, has a number of advantages and disadvantages. One advantage of thermal ink jets is their compact design for the integrated electronics section of the printhead. Thermal ink jets are disadvantageous in that the thermal ink has a tendency to soak into a plain paper medium. This blurs the print or thins out the print locally thereby adversely affecting print quality. Problems have been encountered with thermal ink jets in attempting to rid the ink of moisture fast enough so that the ink does not soak into a plain paper medium. This is particularly true when printing with color. Therefore, usually when printing with thermal ink, one needed to use coated papers, which are more expensive than plain paper.
One advantage of a hot melt ink jet is its ability to print on plain paper since the hot melt ink quickly solidifies as it cools and, since it is waxy in nature, does not normally soak into a paper medium. However, hot melt ink jets can be cumbersome in structure and in design. That is, the associated integrated electronics of a thermal ink jet head are considerably more compact than those of a hot melt ink jet head.
In addition, U.S. Pat. No. 4,751,528, the disclosure of which is totally incorporated herein by reference, discloses a hot melt ink jet system which includes a temperature-controlled platen provided with a heater and a thermoelectric cooler electrically connected to a heat pump and a temperature control unit for controlling the operation of the heater and the heat pump to maintain the platen temperature at a desired level. The apparatus also includes a second thermoelectric cooler to solidify hot melt ink in a selected zone more rapidly to avoid offset by a pinch roll coming in contact with the surface of the substrate to which hot melt ink has been applied. An airtight enclosure surrounding the platen is connected to a vacuum pump and has slits adjacent to the platen to hold the substrate in thermal contact with the platen.
Further, U.S. Pat. No. 4,791,439, the disclosure of which is totally incorporated herein by reference, discloses an apparatus for use with hot melt inks having an integrally connected ink jet head and reservoir system, the reservoir system including a highly efficient heat conducting plate inserted within an essentially non-heat conducting reservoir housing. The reservoir system has a sloping flow path between an inlet position and a sump from which ink is drawn to the head, and includes a plurality of vanes situated upon the plate for rapid heat transfer.
Ink compositions for ink jet printing are known. For example, U.S. Pat. No. 4,840,674, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises a major amount of water, an organic solvent selected from the group consisting of tetramethylene sulfone, 1,1,3,3-tetramethyl urea, 3-methyl sulfolane, and 1,3-dimethyl-2-imidazolidone, which solvent has permanently dissolved therein spirit soluble dyes.
U.S. Pat. No. 5,006,170 and U.S. Pat. No. 5,122,187, the disclosures of each of which are totally incorporated herein by reference, disclose hot melt ink compositions suitable for ink jet printing which comprise a colorant, a binder, and a propellant selected from the group consisting of hydrazine, cyclic amines, ureas, carboxylic acids, sulfonic acids, aldehydes, ketones, hydrocarbons, esters, phenols, amides, imides, halocarbons, urethanes, ethers, sulfones, sulfamides, sulfonamides, phosphites, phosphonates, phosphates, alkyl sulfides, alkyl acetates, and sulfur dioxide.
U.S. Pat. No. 5,021,802, the disclosure of which is totally incorporated herein by reference, discloses a bubble jet ink which comprises 90 to 99.9 percent by weight of aqueous sol-gel medium and 0.1 to 1 percent by weight of colorant. The inks are thermally reversible sol-gels which are gels at ambient temperatures and form liquid sols at temperatures between about 40 and 100.degree. C.
U.S. Pat. No. 5,041,161, the disclosure of which is totally incorporated herein by reference, discloses an ink jet ink which is semi-solid at room temperature. The ink combines the advantageous properties of thermal phase change inks and liquid inks. The inks can comprise vehicles, such as glyceryl esters, polyoxyethylene esters, waxes, fatty acids, and mixtures thereof, which are semi-solid at temperatures between 20.degree. C. and 45.degree. C. The ink is impulse jetted at an elevated temperature in the range of above 45.degree. C. to about 110.degree. C., at which temperature the ink has a viscosity of about 10 to 15 centipoise.
U.S. Pat. No. 4,853,036 and U.S. Pat. No. 5,124,718 disclose an ink for ink jet recording which comprises a liquid composition essentially comprising a coloring matter, a volatile solvent having a vapor pressure of 1 millimeters Hg or more at 25.degree. C., and a material being solid at room temperature and having a molecular weight of 300 or more, and prepared so as to satisfy the formula B.sub.1 /A.sub.1 .gtoreq.3, assuming viscosity as A.sub.1 cP at 25.degree. C., measured when the content of the solid material in the composition is 10 percent by weight, and assuming viscosity as B.sub.1 cP at 25.degree. C., measured when the content of the solid material in the composition is 30 percent by weight. An ink jet recording process using the ink is also disclosed.
U.S. Pat. No. 5,065,167, the disclosure of which is totally incorporated herein by reference, discloses an ink jet ink including a waxy carrier that is solid at 25.degree. C. and liquid at the operating temperature of an ink jet nozzle and a driver having a critical pressure greater than 10 atmospheres, the carrier and driver being miscible in liquid phase.
U.S. Pat. No. 5,047,084, the disclosure of which is totally incorporated herein by reference, discloses an ink jet ink in the form of a microemulsion of an organic vehicle phase comprising fatty acid and colorant dispersed therein and an aqueous phase containing a surfactant, the vehicle phase preferably being liquid at 70.degree. C. and solid at 20.degree. C.
U.S. Pat. No. 5,226,957, the disclosure of which is totally incorporated herein by reference, discloses water insoluble dyes formulated in a microemulsion-based ink which is waterfast, non-threading, and bleed-alleviated. The inks comprise (a) about 0.05 to 0.75 weight percent of a high molecular weight colloid, (b) about 0.1 to 40 weight percent of at least two surfactants, comprising at least one surfactant and at least one co-surfactant, (c) about 0.5 to 20 weight percent of at least one cosolvent, (d) about 0.1 to 5 weight percent of at least one water insoluble dye, (e) about 0.1 to 20 weight percent of an oil, and (f) the balance water. The ink forms a stable microemulsion. "Stabilization of Inverse Micelles by Nonionic Surfactants," Stig E. Friberg, contained in Interfacial Phenomena in Apolar Media, Eicke & Parfitt, eds., Marcel Dekker Inc. (New York and Basel 1987), the disclosure of which is totally incorporated herein by reference, discloses and describes systems with hydrocarbon, water, and nonionic polyalkylene glycol alkyl ether surfactants which display pronounced variation of their phase patterns with temperature. At particular temperatures and component concentrations, a lamellar liquid crystalline phase is observed.
In acoustic ink printing, the print head produces, for example, approximately 2.2 picoliter droplets by an acoustic energy process. The ink under these conditions should display a melt viscosity of about 5 centipoise or less at the jetting temperature. Furthermore, once the ink is jetted onto the paper, the ink image should be of excellent crease property, non-smearing, waterfast, of excellent transparency and fix qualities. In selecting an ink for such applications, it is desirable that the vehicle display low melt viscosity, such as from about 1 centipoise to about 20 centipoise in the acoustic head, while displaying solid like properties after being jetted onto paper. Since the acoustic head can tolerate a temperature up to about 180.degree. C., and preferably up to a temperature of from about 140.degree. C. to about 160.degree. C., the vehicle should display liquid like properties such as a viscosity of 1 to about 20 centipoise at a temperature of from about 125.degree. C. to about 165.degree. C., and solidify or harden after jetting onto paper such that the ink displays a hardness value of from about less than 0.1 to 2.0 millimeters utilizing a penetrometer according to the ASTM penetration method D1321. The hot melt inks of this invention with the triblock copolymer structure have advantages over the prior art hot melt inks, such as those with ester modified waxes (U.S. Pat. No. 4,851,045), polyoxyethylene esters (U.S. Pat. No. 5,041,161), benzene sulfonamide (U.S. Pat. No. 5,230,731), mono amides (U.S. Pat. No. 4,889,560) and polyethylene waxes (U.S. Pat. No. 5,185,035), which advantages include the use of a triblock structure for the ink vehicle, and which inks display a viscosity of from about 1 to about 20 centipoise when heated to a temperature of from about 125.degree. C. to 180.degree. C., such that the acoustic energy in the printhead can eject an ink droplet onto paper. For example, preferred triblock structures include JEFFAMINE D-400.TM. distearate, JEFFAMINE ED-600.TM. distearate and JEFFAMINE ED-900.TM. distearate. The viscosities of these materials at 160.degree. C. are 6, 8, and 10 centipoise, respectively. Another advantage of these vehicles is that they have a high hardness or low penetration value, and thereby enable excellent image permanence. For example, the penetration/hardness value of the JEFFAMINE D-400.TM. distearate is 0.8 millimeter.
Curable inks are known, for example, U.S. Pat. No. 4,680,368 discloses an ultraviolet curable ink composition comprising a polyurethane polymethacrylate obtained by reacting a polyisocyanate compound of the formula ##STR1## wherein R.sub.1 is a hydrogen atom or a methyl group, and n is an integer of from 1 to 20, with a hydroxyl group containing methacrylate and having in one molecule at least two methacryloyl groups and at least two urethane bonds, a radical polymerizable low molecular weight compound, and a photopolymerization initiator. In addition, U.S. Pat. No. 4,443,495 discloses a heat curable conductive ink that comprises (1) an ethylenically unsaturated member of the group consisting of (a) a liquid ethylenically unsaturated monomer or oligomer of the formula ##STR2## wherein R is H or CH.sub.3, R.sub.1 is an organic moiety and n is at least 2, (b) a polythiol in combination with (a), (c) a polythiol in combination with a liquid ethylenically unsaturated monomer or oligomer of the formula ##STR3## wherein R.sub.2 is H or CH.sub.3, R.sub.3 is an organic moiety and n is at least 2, and (d) mixtures of (a), (b), and (c); (2) a thermal initiator; and (3) an electrically conductive material. Heating of the composition in a desired pattern on a substrate results in a printed electric circuit.
Microemulsion ink compositions are illustrated in U.S. Pat. No. 5,492,559, the disclosure of which is totally incorporated herein by reference.
Disclosed in U.S. Pat. Nos. 5,688,312; 5,667,568; 5,700,316 and 5,747,554, the disclosures of each being totally incorporated herein by reference are acoustic ink jet inks and processes thereof.
While known compositions and processes are suitable for their intended purposes, a need remains for acoustic hot melt ink compositions suitable for acoustic ink jet printing. In addition, there is a need for hot melt ink compositions which are compatible with a wide variety of plain papers. Further, there is a need for hot melt ink compositions which generate high quality, waterfast images on plain papers. There is also a need for hot melt ink jet ink compositions which generate high quality, fast-drying images on a wide variety of plain papers at low cost, with high quality text and high quality graphics. Further, there is a need for hot melt ink jet ink compositions which exhibit minimal feathering. Additionally, there is a need for hot melt ink jet ink compositions which exhibit minimal intercolor bleed. There is also a need for hot melt ink jet ink compositions which exhibit excellent image permanence. Further, there is a need for hot melt ink jet ink compositions which are suitable for use in acoustic ink jet printing processes. Additionally, there is a need for hot ink compositions suitable for ink jet printing processes wherein the substrate is heated prior to printing and is cooled to ambient temperature subsequent to printing (also known as heat and delay printing processes). There is also a need for ink compositions suitable for ink jet printing wherein high optical densities can be achieved with relatively low dye concentrations. A need also remains for ink compositions suitable for ink jet printing wherein curling of the substrate subsequent to printing is minimized, or avoided.